Activity based Contrast Enhancement of Compressed Digital images in DCT Domain

In most image enhancement tasks, contrast enhancement is a pre-step for the later processing stages. In this paper, we propose a new technique for adaptive contrast enhancement of compressed images in discrete cosine transform (DCT) domain. The algorithm, at the same time, uses human visual system (HVS) as a guide in avoiding unpleasant block artifacts that often appear at the Hock boundaries as a result of processing in DCT domain. An activity measure determines the level of enhancement that a block can withstand without creating any blocking artifacts and simultaneously enhancing the contrast. Since the enhancement process is done during the decompression stage, the compressibility of the original image is not affected. Subjective and objective tests validate our concept of activity based contrast enhancement and the avoidance of block artifacts in the resultant image.